Oil is included in industrial wastewater effluent from an industrial society system such as a food plant. This oil is subjected to: a flocculation treatment using a flocculation agent that contains iron, aluminum salt, and the like; or a floatation treatment utilizing the adhesion properties of the oil to fine air bubbles. Through these treatments, the oil is disposed of as an industrial waste in the form of oil-containing polluted sludge. From the viewpoint of the necessity of reducing the generation of polluted sludge and selectively oil removal needs from industrial wastewater, technologies for oil removal by use of an oil adsorbent have been proposed as water treatment systems configured to treat water including oil, in addition to the above-mentioned oil removal technologies.
For selective removal of oil, Patent Document 1 proposes a technology of oil removal from water to be treated (hereinafter referred to as “to-be-treated water”) by bringing the to-be-treated water into contact with an oil-water separation medium whose surface properties have a high affinity with oil. Patent Document 1 further proposes a technology in which: air bubbles are introduced into the oil-water separation medium having adsorbed the oil; thereby, the oil is removed from to-be-treated water; and thus, the oil-water separation medium is recovered.
Patent Document 2 proposes: an oil removal method using a magnetic substance for adsorbing oil which floats on the surface of water; and a method of recovering the magnetic substance by use of a magnetic force. This technology may be used as a method of recovering oil in a water treatment operation conducted in a large area, such as a sea.
Patent Document 3 discloses a technology in which: oil is adsorbed to hydrophobic-surface particles each having a magnetic substance as its core material; and thereafter the hydrophobic-surface particles are flocculated by use of a flocculation agent. According to the technology disclosed in Patent Document 3, the adsorbent is thereafter reused through the regeneration of the adsorbent by use of a solvent, or in the form of burning the adsorbent.